Monocrystalline solid state materials such as single-crystal semiconductors are the basis of the current microelectronics industry. Solid state materials are characterized by a variety of properties, for example, electrical properties such as electrical conductivity or charge mobility, optical properties such as refractive index or speed of photons, thermal properties such as thermal conductivity or thermal expansion, mechanical properties such as stress or strain curves, and chemical properties such as resistance to corrosion or reaction consistency, among others.
Over the past years, the semiconductor industry has constantly explored new ways of increasing the amount of active surface area on the integrated circuit chips, particularly on those employing monocrystalline semiconductor substrates. Accordingly, attempts to modify the electrical, optical, thermal and/or mechanical properties of such monocrystalline substrates have been made in an effort to minimize the dimensions of the IC devices, while maximizing the corresponding available active area. For example, new epitaxial growth processes such as the Epitaxial Lateral Overgrowth (ELO) have been used in an attempt to extend the amount of surface area available to active devices. However, these growth processes have limited results mainly because they consume part of the precious surface areas for seeding purposes, defeating therefore the primary purpose of increasing the available active area.
Another technology proposed by the semiconductor industry is the so-called Silicon-On-Insulator (SOI) process, wherein oxygen atoms are implanted at high dose and energy to form a silicon dioxide insulating layer between the upper surface of the original monocrystalline substrate and the bottom bulk portion of the same substrate. Although the SOI devices have many advantages, such as reduced parasitic capacitance due to the buried insulating layer, the process is relatively expensive because of the high costs of implanting the oxygen atoms and curing of the implant-induced defects.
Thin-film technology, including the formation of multi-layered dielectrics, is another highly developed technology in the semiconductor industry, which is widely used for the control of the reflection and/or transmission of light or radiant heat at optical surfaces. When monochromatic light falls on a thin transparent film dielectric having a thickness “d,” the light waves reflected from the front and the rear surfaces of the dielectric film interfere. For near-normal incidence, the conditions for a maximum or minimum intensity of the light reflected from such film dielectric depend on the index of refraction of the film dielectric as follows:2nd=(k+½)λ maxima  (1)
and2nd=kλ minima  (2)
wherein: n=index of refraction of the dielectric;
λ=wavelength of a monochromatic light entering the dielectric;
d=thickness of the dielectric; and
k=0, 1, 2, . . .
Equations (1) and (2) apply when the index of refraction “n” of the dielectric film is greater or less than the indices of the media on each side of the dielectric. Only in these cases, there will be a relative phase change of 180° for reflections at the two surfaces. A glass plate in air or an air film between two glass plates provide examples of cases to which both equations (1) and (2) apply.
Accordingly, there is a need for an improved method of increasing the available active surface area on integrated circuit chips fabricated on monocrystalline substrates which involve the transmission and/or reflection of light. There is also a need for a more advantageous method of forming dielectric mirrors in monocrystalline semiconducting substrates for low power dissipation, low light losses and high speed optoelectronic devices.